1
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Araujo CILD, Virtanen P, Spies M, González-Orellana C, Kerschbaumer S, Ilyn M, Rogero C, Heikkilä TT, Giazotto F, Strambini E. Superconducting spintronic heat engine. Nat Commun 2024; 15:4823. [PMID: 38844436 PMCID: PMC11156981 DOI: 10.1038/s41467-024-49052-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 05/23/2024] [Indexed: 06/09/2024] Open
Abstract
Heat engines are key devices that convert thermal energy into usable energy. Strong thermoelectricity, at the basis of electrical heat engines, is present in superconducting spin tunnel barriers at cryogenic temperatures where conventional semiconducting or metallic technologies cease to work. Here we realize a superconducting spintronic heat engine consisting of a ferromagnetic insulator/superconductor/insulator/ferromagnet tunnel junction (EuS/Al/AlOx/Co). The efficiency of the engine is quantified for bath temperatures ranging from 25 mK up to 800 mK, and at different load resistances. Moreover, we show that the sign of the generated thermoelectric voltage can be inverted according to the parallel or anti-parallel orientation of the two ferromagnetic layers, EuS and Co. This realizes a thermoelectric spin valve controlling the sign and strength of the Seebeck coefficient, thereby implementing a thermoelectric memory cell. We propose a theoretical model that allows describing the experimental data and predicts the engine efficiency for different device parameters.
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Affiliation(s)
- Clodoaldo Irineu Levartoski de Araujo
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy
- Departamento de Fìsica, Laboratório de Spintrônica e Nanomagnetismo, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil
| | - Pauli Virtanen
- Department of Physics and Nanoscience Center, University of Jyväskylä, Jyväskylä, Finland.
| | - Maria Spies
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy
| | - Carmen González-Orellana
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Donostia-San Sebastián, Spain
| | - Samuel Kerschbaumer
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Donostia-San Sebastián, Spain
| | - Maxim Ilyn
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Donostia-San Sebastián, Spain
| | - Celia Rogero
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Donostia-San Sebastián, Spain
- Donostia International Physics Center (DIPC), Donostia-San Sebastián, Spain
| | - Tero Tapio Heikkilä
- Department of Physics and Nanoscience Center, University of Jyväskylä, Jyväskylä, Finland
| | - Francesco Giazotto
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy
| | - Elia Strambini
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy.
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2
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González-Ruano C, Caso D, Ouassou JA, Tiusan C, Lu Y, Linder J, Aliev FG. Observation of Magnetic State Dependent Thermoelectricity in Superconducting Spin Valves. PHYSICAL REVIEW LETTERS 2023; 130:237001. [PMID: 37354396 DOI: 10.1103/physrevlett.130.237001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 03/03/2023] [Accepted: 05/08/2023] [Indexed: 06/26/2023]
Abstract
Superconductor-ferromagnet tunnel junctions demonstrate giant thermoelectric effects that are being exploited to engineer ultrasensitive terahertz radiation detectors. Here, we experimentally observe the recently predicted complete magnetic control over thermoelectric effects in a superconducting spin valve, including the dependence of its sign on the magnetic state of the spin valve. The description of the experimental results is improved by the introduction of an interfacial domain wall in the spin filter layer interfacing the superconductor. Surprisingly, the application of high in-plane magnetic fields induces a double sign inversion of the thermoelectric effect, which exhibits large values even at applied fields twice the superconducting critical field.
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Affiliation(s)
- César González-Ruano
- Departamento Física de la Materia Condensada C-III, Universidad Autónoma de Madrid, Madrid 28049, Spain
| | - Diego Caso
- Departamento Física de la Materia Condensada C-III, Universidad Autónoma de Madrid, Madrid 28049, Spain
| | - Jabir Ali Ouassou
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-M7T9Q Trondheim, Norway
| | - Coriolan Tiusan
- Department of Solid State Physics and Advanced Technologies, Faculty of Physics, Babes-Bolyai University, Cluj Napoca 400114, Romania
- Institut Jean Lamour, Nancy Universitè, 54506 Vandoeuvre-les-Nancy Cedex, France
| | - Yuan Lu
- Institut Jean Lamour, Nancy Universitè, 54506 Vandoeuvre-les-Nancy Cedex, France
| | - Jacob Linder
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-M7T9Q Trondheim, Norway
| | - Farkhad G Aliev
- Departamento Física de la Materia Condensada C-III, Instituto Nicolás Cabrera (INC) and Condensed Matter Physics Institute (IFIMAC), Universidad Autónoma de Madrid, Madrid 28049, Spain
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3
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Turkin YV, Pugach N. Spin dynamics in superconductor/ferromagnetic insulator hybrid structures with precessing magnetization. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2023; 14:233-239. [PMID: 36865092 PMCID: PMC9972883 DOI: 10.3762/bjnano.14.22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Accepted: 02/06/2023] [Indexed: 06/18/2023]
Abstract
The main goal of the present work is the description of the dynamics of spin current and induced magnetization inside a superconducting film S that is in contact with a ferromagnetic insulator layer FI. Spin current and induced magnetization are calculated not only at the interface of the S/FI hybrid structure, but also inside the superconducting film. The new and interesting predicted effect is the frequency dependence of the induced magnetization with a maximum appearing at high temperatures. It is also shown that the increase of the magnetization precession frequency can drastically change the spin distribution of quasiparticles at the S/FI interface.
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Affiliation(s)
- Yaroslav V Turkin
- HSE University, Moscow 101000, Russia
- Vernadsky Crimean Federal University, Simferopol 295007
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4
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Karabassov T, Pashkovskaia VD, Parkhomenko NA, Guravova AV, Kazakova EA, Lvov BG, Golubov AA, Vasenko AS. Density of states in the presence of spin-dependent scattering in SF bilayers: a numerical and analytical approach. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2022; 13:1418-1431. [PMID: 36540701 PMCID: PMC9732889 DOI: 10.3762/bjnano.13.117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Accepted: 11/07/2022] [Indexed: 06/17/2023]
Abstract
We present a quantitative study of the density of states (DOS) in SF bilayers (where S is a bulk superconductor and F is a ferromagnetic metal) in the diffusive limit. We solve the quasiclassical Usadel equations in the structure considering the presence of magnetic and spin-orbit scattering. For practical reasons, we propose the analytical solution for the density of states in SF bilayers in the case of a thin ferromagnet and low transparency of the SF interface. This solution is confirmed by numerical calculations using a self-consistent two-step iterative method. The behavior of DOS dependencies on magnetic and spin-orbit scattering times is discussed.
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Affiliation(s)
| | | | | | | | - Elena A Kazakova
- Sechenov First Moscow State Medical University, 119991 Moscow, Russia
| | | | - Alexander A Golubov
- Faculty of Science and Technology and MESA Institute for Nanotechnology, University of Twente, 7500 AE Enschede, Netherlands
- Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia
| | - Andrey S Vasenko
- HSE University, 101000 Moscow, Russia
- I. E. Tamm Department of Theoretical Physics, P. N. Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow, Russia
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5
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Germanese G, Paolucci F, Marchegiani G, Braggio A, Giazotto F. Bipolar thermoelectric Josephson engine. NATURE NANOTECHNOLOGY 2022; 17:1084-1090. [PMID: 36138204 DOI: 10.1038/s41565-022-01208-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Accepted: 07/26/2022] [Indexed: 06/16/2023]
Abstract
Thermoelectric effects in metals are typically small due to the nearly perfect particle-hole symmetry around their Fermi surface. Furthermore, thermo-phase effects and linear thermoelectricity in superconducting systems have been identified only when particle-hole symmetry is explicitly broken, since thermoelectric effects were considered impossible in pristine superconductors. Here, we experimentally demonstrate that superconducting tunnel junctions develop a very large bipolar thermoelectricity in the presence of a sizable thermal gradient thanks to spontaneous particle-hole symmetry breaking. Our junctions show Seebeck coefficients of up to ±300 μV K-1, which is comparable with quantum dots and roughly 105 times larger than the value expected for normal metals at subkelvin temperatures. Moreover, by integrating our junctions into a Josephson interferometer, we realize a bipolar thermoelectric Josephson engine generating phase-tunable electric powers of up to ~140 nW mm-2. Notably, our device implements also the prototype for a persistent thermoelectric memory cell, written or erased by current injection. We expect that our findings will lead to applications in superconducting quantum technologies.
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Affiliation(s)
- Gaia Germanese
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy
- Dipartimento di Fisica, Università di Pisa, Pisa, Italy
| | - Federico Paolucci
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy.
| | | | - Alessandro Braggio
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy
| | - Francesco Giazotto
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy.
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6
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Machon P, Wolf MJ, Beckmann D, Belzig W. Experimental and theoretical study of field-dependent spin splitting at ferromagnetic insulator-superconductor interfaces. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2022; 13:682-688. [PMID: 35957675 PMCID: PMC9344541 DOI: 10.3762/bjnano.13.60] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Accepted: 06/08/2022] [Indexed: 06/15/2023]
Abstract
We present a combined experimental and theoretical work that investigates the magnetic proximity effect at a ferromagnetic insulator-superconductor (FI-S) interface. The calculations are based on the boundary condition for diffusive quasiclassical Green's functions, which accounts for arbitrarily strong spin-dependent effects and spin mixing angles. The resulting phase diagram shows a transition from a first-order to a second-order phase transition for large spin mixing angles. The experimentally found differential conductance of an EuS-Al heterostructure is compared with the theoretical calculation. With the assumption of a uniform spin mixing angle that depends on the externally applied field, we find good agreement between theory and experiment. The theory depends only on very few parameters, mostly specified by the experimental setup. We determine the effective spin of the interface moments as J ≈ 0.74ℏ.
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Affiliation(s)
- Peter Machon
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
| | - Michael J Wolf
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
- present address: Institute for Technical Physics, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
| | - Detlef Beckmann
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
| | - Wolfgang Belzig
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
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7
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Strambini E, Spies M, Ligato N, Ilić S, Rouco M, González-Orellana C, Ilyn M, Rogero C, Bergeret FS, Moodera JS, Virtanen P, Heikkilä TT, Giazotto F. Superconducting spintronic tunnel diode. Nat Commun 2022; 13:2431. [PMID: 35508475 PMCID: PMC9068691 DOI: 10.1038/s41467-022-29990-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 04/11/2022] [Indexed: 11/09/2022] Open
Abstract
Diodes are key elements for electronics, optics, and detection. Their evolution towards low dissipation electronics has seen the hybridization with superconductors and the realization of supercurrent diodes with zero resistance in only one direction. Here, we present the quasi-particle counterpart, a superconducting tunnel diode with zero conductance in only one direction. The direction-selective propagation of the charge has been obtained through the broken electron-hole symmetry induced by the spin selection of the ferromagnetic tunnel barrier: a EuS thin film separating a superconducting Al and a normal metal Cu layer. The Cu/EuS/Al tunnel junction achieves a large rectification (up to ∼40%) already for a small voltage bias (∼200 μV) thanks to the small energy scale of the system: the Al superconducting gap. With the help of an analytical theoretical model we can link the maximum rectification to the spin polarization (P) of the barrier and describe the quasi-ideal Shockley-diode behavior of the junction. This cryogenic spintronic rectifier is promising for the application in highly-sensitive radiation detection for which two different configurations are evaluated. In addition, the superconducting diode may pave the way for future low-dissipation and fast superconducting electronics.
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Affiliation(s)
- E Strambini
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127, Pisa, Italy.
| | - M Spies
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127, Pisa, Italy.
| | - N Ligato
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127, Pisa, Italy
| | - S Ilić
- Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, E-20018, Donostia-San Sebastián, Spain
| | - M Rouco
- Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, E-20018, Donostia-San Sebastián, Spain
| | - Carmen González-Orellana
- Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, E-20018, Donostia-San Sebastián, Spain
| | - Maxim Ilyn
- Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, E-20018, Donostia-San Sebastián, Spain
| | - Celia Rogero
- Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, E-20018, Donostia-San Sebastián, Spain
- Donostia International Physics Center (DIPC), E-20018, Donostia-San Sebastián, Spain
| | - F S Bergeret
- Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, E-20018, Donostia-San Sebastián, Spain
- Donostia International Physics Center (DIPC), E-20018, Donostia-San Sebastián, Spain
| | - J S Moodera
- Physics Department and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - P Virtanen
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35 (YFL), FI-40014, Jyväskylä, Finland
| | - T T Heikkilä
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35 (YFL), FI-40014, Jyväskylä, Finland
| | - F Giazotto
- NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127, Pisa, Italy.
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8
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Tan ZB, Laitinen A, Kirsanov NS, Galda A, Vinokur VM, Haque M, Savin A, Golubev DS, Lesovik GB, Hakonen PJ. Thermoelectric current in a graphene Cooper pair splitter. Nat Commun 2021; 12:138. [PMID: 33420055 PMCID: PMC7794233 DOI: 10.1038/s41467-020-20476-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 11/29/2020] [Indexed: 11/17/2022] Open
Abstract
Generation of electric voltage in a conductor by applying a temperature gradient is a fundamental phenomenon called the Seebeck effect. This effect and its inverse is widely exploited in diverse applications ranging from thermoelectric power generators to temperature sensing. Recently, a possibility of thermoelectricity arising from the interplay of the non-local Cooper pair splitting and the elastic co-tunneling in the hybrid normal metal-superconductor-normal metal structures was predicted. Here, we report the observation of the non-local Seebeck effect in a graphene-based Cooper pair splitting device comprising two quantum dots connected to an aluminum superconductor and present a theoretical description of this phenomenon. The observed non-local Seebeck effect offers an efficient tool for producing entangled electrons. Thermoelectricity due to the interplay of the nonlocal Cooper pair splitting and the elastic co-tunneling in normal metal-superconductor-normal metal structure is predicted. Here, the authors observe the non-local Seebeck effect in a graphene-based Cooper pair splitting device.
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Affiliation(s)
- Z B Tan
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland.,Shenzhen Institute for Quantum Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China
| | - A Laitinen
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland
| | - N S Kirsanov
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland.,Terra Quantum AG, St. Gallerstrasse 16A, 9400, Rorschach, Switzerland.,Moscow Institute of Physics and Technology, Institutskii Per. 9, Dolgoprudny, Moscow Distr., 141700, Russian Federation.,Consortium for Advanced Science and Engineering (CASE), University of Chicago, 5801 S Ellis Avenue, Chicago, IL, 60637, USA
| | - A Galda
- James Franck Institute, University of Chicago, Chicago, IL, 60637, USA.,Materials Science Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL, 60439, USA
| | - V M Vinokur
- Consortium for Advanced Science and Engineering (CASE), University of Chicago, 5801 S Ellis Avenue, Chicago, IL, 60637, USA.,Materials Science Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL, 60439, USA
| | - M Haque
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland
| | - A Savin
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland
| | - D S Golubev
- QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| | - G B Lesovik
- Terra Quantum AG, St. Gallerstrasse 16A, 9400, Rorschach, Switzerland.,Moscow Institute of Physics and Technology, Institutskii Per. 9, Dolgoprudny, Moscow Distr., 141700, Russian Federation
| | - P J Hakonen
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland. .,QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland.
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9
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Kuzmanović M, Wu BY, Weideneder M, Quay CHL, Aprili M. Evidence for spin-dependent energy transport in a superconductor. Nat Commun 2020; 11:4336. [PMID: 32859913 PMCID: PMC7455713 DOI: 10.1038/s41467-020-18161-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 07/31/2020] [Indexed: 11/20/2022] Open
Abstract
In ferromagnetic materials, spin up and down electrons can carry different heat currents. This spin-dependent energy excitation mode ('spin energy mode') occurs only when spin up and down energy distribution functions are different. In superconductors, heat is carried by quasiparticle excitations and the spin energy mode can be excited by spin-polarised current injection. In the presence of a finite Zeeman magnetic field, the spin energy mode surprisingly leads to a charge imbalance (different numbers of hole- and electron-like quasiparticles) at the superconducting gap edge. By performing spin-resolved spectroscopy of the out-of-equilibrium quasiparticle populations in a mescoscopic superconductor, we reveal that their distribution functions are non-Fermi-Dirac. In addition, our spectroscopic technique allows us to observe a charge imbalance, localised in energy to the gap edge and thus unambiguously identify the spin energy mode. Our results agree well with theory and shed light on energy transport in superconducting spintronics.
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Affiliation(s)
- M Kuzmanović
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
| | - B Y Wu
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
- Graduate Institute of Applied Physics, National Taiwan University, Taipei, 10617, Taiwan
| | - M Weideneder
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
- Institute for Experimental and Applied Physics, University of Regensburg, 93053, Regensburg, Germany
| | - C H L Quay
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France.
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
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10
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Blasi G, Taddei F, Arrachea L, Carrega M, Braggio A. Nonlocal Thermoelectricity in a Superconductor-Topological-Insulator-Superconductor Junction in Contact with a Normal-Metal Probe: Evidence for Helical Edge States. PHYSICAL REVIEW LETTERS 2020; 124:227701. [PMID: 32567914 DOI: 10.1103/physrevlett.124.227701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 02/05/2020] [Accepted: 05/15/2020] [Indexed: 06/11/2023]
Abstract
We consider a Josephson junction hosting a Kramers pair of helical edge states of a quantum spin Hall bar in contact with a normal-metal probe. In this hybrid system, the orbital phase, induced by a small magnetic field threading the junction known as a Doppler shift, combines with the conventional Josephson phase difference and originates an effect akin to a Zeeman field in the spectrum. As a consequence, when a temperature bias is applied to the superconducting terminals, a thermoelectric current is established in the normal probe. We argue that this purely nonlocal thermoelectric effect is a unique signature of the helical nature of the edge states coupled to superconducting leads and it can constitute a useful tool for probing the helical nature of the edge states in systems where the Hall bar configuration is difficult to achieve. We fully characterize thermoelectric response and performance of this hybrid junction in a wide range of parameters, demonstrating that the external magnetic flux inducing the Doppler shift can be used as a knob to control the thermoelectric response and the heat flow in a novel device based on topological junctions.
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Affiliation(s)
- Gianmichele Blasi
- NEST, Scuola Normale Superiore and Instituto Nanoscienze-CNR, I-56126 Pisa, Italy
| | - Fabio Taddei
- NEST, Scuola Normale Superiore and Instituto Nanoscienze-CNR, I-56126 Pisa, Italy
| | - Liliana Arrachea
- International Center for Advanced Studies, ECyT-UNSAM, Campus Miguelete, 25 de Mayo y Francia, 1650 Buenos Aires, Argentina
| | - Matteo Carrega
- NEST, Scuola Normale Superiore and Instituto Nanoscienze-CNR, I-56126 Pisa, Italy
| | - Alessandro Braggio
- NEST, Scuola Normale Superiore and Instituto Nanoscienze-CNR, I-56126 Pisa, Italy
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11
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Marchegiani G, Braggio A, Giazotto F. Nonlinear Thermoelectricity with Electron-Hole Symmetric Systems. PHYSICAL REVIEW LETTERS 2020; 124:106801. [PMID: 32216390 DOI: 10.1103/physrevlett.124.106801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 02/05/2020] [Accepted: 02/14/2020] [Indexed: 06/10/2023]
Abstract
In the linear regime, thermoelectric effects between two conductors are possible only in the presence of an explicit breaking of the electron-hole symmetry. We consider a tunnel junction between two electrodes and show that this condition is no longer required outside the linear regime. In particular, we demonstrate that a thermally biased junction can display an absolute negative conductance, and hence thermoelectric power, at a small but finite voltage bias, provided that the density of states of one of the electrodes is gapped and the other is monotonically decreasing. We consider a prototype system that fulfills these requirements, namely, a tunnel junction between two different superconductors where the Josephson contribution is suppressed. We discuss this nonlinear thermoelectric effect based on the spontaneous breaking of electron-hole symmetry in the system, characterize its main figures of merit, and discuss some possible applications.
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Affiliation(s)
- G Marchegiani
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
| | - A Braggio
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
| | - F Giazotto
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
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12
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Kamra A, Rezaei A, Belzig W. Spin Splitting Induced in a Superconductor by an Antiferromagnetic Insulator. PHYSICAL REVIEW LETTERS 2018; 121:247702. [PMID: 30608749 DOI: 10.1103/physrevlett.121.247702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Indexed: 06/09/2023]
Abstract
Inspired by recent feats in exchange coupling antiferromagnets to an adjacent material, we demonstrate the possibility of employing them for inducing spin splitting in a superconductor, thereby avoiding the detrimental, parasitic effects of ferromagnets employed to this end. We derive the Gor'kov equation for the matrix Green's function in the superconducting layer, considering a microscopic model for its disordered interface with a two-sublattice magnetic insulator. We find that an antiferromagnetic insulator with effectively uncompensated interface induces a large, disorder-resistant spin splitting in the adjacent superconductor. In addition, we find contributions to the self-energy stemming from the interfacial disorder. Within our model, these mimic impurity and spin-flip scattering, while another breaks the symmetries in particle-hole and spin spaces. The latter contribution, however, drops out in the quasiclassical approximation and thus, does not significantly affect the superconducting state.
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Affiliation(s)
- Akashdeep Kamra
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Ali Rezaei
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
| | - Wolfgang Belzig
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
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13
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De Simoni G, Strambini E, Moodera JS, Bergeret FS, Giazotto F. Toward the Absolute Spin-Valve Effect in Superconducting Tunnel Junctions. NANO LETTERS 2018; 18:6369-6374. [PMID: 30248266 DOI: 10.1021/acs.nanolett.8b02723] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A superconductor with a spin-split excitation spectrum behaves as an ideal ferromagnetic spin-injector in a tunneling junction. It was theoretically predicted that the combination of two such spin-split superconductors with independently tunable magnetizations may be used as an ideal absolute spin-valve. Here, we report on the first switchable superconducting spin-valve based on two EuS/Al bilayers coupled through an aluminum oxide tunnel barrier. The spin-valve shows a relative resistance change between the parallel and antiparallel configuration of the EuS layers up to 900% that demonstrates a highly spin-polarized current through the junction. Our device may be pivotal for realization of thermoelectric radiation detectors, a logical element for a memory cell in cryogenics, superconductor-based computers, and superconducting spintronics in general.
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Affiliation(s)
- Giorgio De Simoni
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore , I-56127 Pisa , Italy
| | - Elia Strambini
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore , I-56127 Pisa , Italy
| | - Jagadeesh S Moodera
- Department of Physics, Francis Bitter Magnet Lab and Plasma Science and Fusion Center , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - F Sebastian Bergeret
- Centro de Fisica de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU , Manuel de Lardizabal 5 , E-20018 San Sebastian , Spain
- Donostia International Physics Center (DIPC) , Manuel de Lardizabal 4 , E-20018 San Sebastian , Spain
| | - Francesco Giazotto
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore , I-56127 Pisa , Italy
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14
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Komori S, Di Bernardo A, Buzdin AI, Blamire MG, Robinson JWA. Magnetic Exchange Fields and Domain Wall Superconductivity at an All-Oxide Superconductor-Ferromagnet Insulator Interface. PHYSICAL REVIEW LETTERS 2018; 121:077003. [PMID: 30169105 DOI: 10.1103/physrevlett.121.077003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 05/20/2018] [Indexed: 06/08/2023]
Abstract
At a superconductor-ferromagnet (S/F) interface, the F layer can introduce a magnetic exchange field within the S layer, which acts to locally spin split the superconducting density of states. The effect of magnetic exchange fields on superconductivity has been thoroughly explored at S-ferromagnet insulator (S/FI) interfaces for isotropic s-wave S and a thickness that is smaller than the superconducting coherence length. Here we report a magnetic exchange field effect at an all-oxide S/FI interface involving the anisotropic d-wave high temperature superconductor praseodymium cerium copper oxide (PCCO) and the FI praseodymium calcium manganese oxide (PCMO). The magnetic exchange field in PCCO, detected via magnetotransport measurements through the superconducting transition, is localized to the PCCO/PCMO interface with an average magnitude that depends on the presence or absence of magnetic domain walls in PCMO. The results are promising for the development of all-oxide superconducting spintronic devices involving unconventional pairing and high temperature superconductors.
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Affiliation(s)
- S Komori
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - A Di Bernardo
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - A I Buzdin
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
- University Bordeaux, LOMA UMR-CNRS 5798, F-33405 Talence Cedex, France
| | - M G Blamire
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - J W A Robinson
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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15
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Beckmann D, Hübler F, Wolf MJ, Löhneysen HV. Andreev bound states at spin-active interfaces. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20150002. [PMID: 29941622 PMCID: PMC6030144 DOI: 10.1098/rsta.2015.0002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/07/2018] [Indexed: 06/08/2023]
Abstract
Andreev bound states are ubiquitous in superconducting hybrid structures. They are formed near impurities, in Josephson junctions, in vortex cores and at interfaces. At spin-active superconductor-ferromagnet interfaces, Andreev bound states are formed due to spin-dependent scattering phases. Spin-dependent phase shifts are an important ingredient for the generation of triplet Cooper pairs in superconductor-ferromagnet hybrid structures. Spectroscopy of Andreev bound states is a powerful probe of superconducting order parameter symmetry, as well as spin-dependent interface scattering and the triplet proximity effect.This article is part of the theme issue 'Andreev bound states'.
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Affiliation(s)
- D Beckmann
- Institut für Nanotechnologie, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
- Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
| | - F Hübler
- Institut für Nanotechnologie, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
- Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
- Institut für Festkörperphysik, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
| | - M J Wolf
- Institut für Nanotechnologie, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
| | - H V Löhneysen
- Physikalisches Institut, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
- Center for Functional Nanostructures (CFN), Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
- Institut für Festkörperphysik, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
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16
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Quay CHL, Aprili M. Out-of-equilibrium spin transport in mesoscopic superconductors. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:rsta.2015.0342. [PMID: 29941629 PMCID: PMC6030150 DOI: 10.1098/rsta.2015.0342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/16/2016] [Indexed: 06/08/2023]
Abstract
The excitations in conventional superconductors, Bogoliubov quasi-particles, are spin-[Formula: see text] fermions but their charge is energy-dependent and, in fact, zero at the gap edge. Therefore, in superconductors (unlike normal metals) spin and charge degrees of freedom may be separated. In this article, we review spin injection into conventional superconductors and focus on recent experiments on mesoscopic superconductors. We show how quasi-particle spin transport and out-of-equilibrium spin-dependent superconductivity can be triggered using the Zeeman splitting of the quasi-particle density of states in thin-film superconductors with small spin-mixing scattering. Finally, we address the spin dynamics and the feedback of quasi-particle spin imbalances on the amplitude of the superconducting energy gap.This article is part of the theme issue 'Andreev bound states'.
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Affiliation(s)
- C H L Quay
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université, Paris-Saclay, 91405 Orsay, France
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université, Paris-Saclay, 91405 Orsay, France
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17
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Eschrig M. Theory of Andreev bound states in S-F-S junctions and S-F proximity devices. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20150149. [PMID: 29941624 PMCID: PMC6030143 DOI: 10.1098/rsta.2015.0149] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/16/2016] [Indexed: 06/08/2023]
Abstract
Andreev bound states are an expression of quantum coherence between particles and holes in hybrid structures composed of superconducting and non-superconducting metallic parts. Their spectrum carries important information on the nature of the pairing, and determines the current in Josephson devices. Here, I focus on Andreev bound states in systems involving superconductors and ferromagnets with strong spin-polarization. I provide a general framework for non-local Andreev phenomena in such structures in terms of coherence functions, and show how the latter link wave function and Green-function based theories.This article is part of the theme issue 'Andreev bound states'.
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Affiliation(s)
- M Eschrig
- Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
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18
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Koley S, Sen S, Chakrabarti S. Vanishing Thermal Conductance of Carbon Nanotube upon Encapsulation by Zigzag Sulfur Chain. J Phys Chem Lett 2018; 9:3105-3109. [PMID: 29788721 DOI: 10.1021/acs.jpclett.8b01121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We report an unprecedented enhancement of thermoelectric properties of a single-walled carbon nanotube upon encapsulation of a zigzag sulfur chain inside the nanocore. Our calculations on a 70 Å long [5, 5] carbon nanotube reveal that the encapsulation of zigzag sulfur chain will lead to a 107% increase in the thermoelectric figure of merit and concomitant quenching of thermal conductance by 90%. We have noticed that finite transmission gradient at the Fermi level combined with destructive quantum interference at the sulfur sites and structural conformation-dependent scattering-induced damping of phonon transmission are attributed to the dramatic improvement of thermoelectric behavior of this material. This finding indeed will help circumvent the long-standing problem in the fabrication of carbon-nanotube-based ultrafast device.
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Affiliation(s)
- Sayantanu Koley
- Department of Chemistry , University of Calcutta , 92, A. P. C. Road , Kolkata 700009 , India
| | - Sabyasachi Sen
- Department of Physics , JIS College of Engineering , Block-A, Phase-III , Kalyani, Nadia PIN-741235 , India
| | - Swapan Chakrabarti
- Department of Chemistry , University of Calcutta , 92, A. P. C. Road , Kolkata 700009 , India
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19
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Sengupta P, Wen Y, Shi J. Spin-dependent magneto-thermopower of narrow-gap lead chalcogenide quantum wells. Sci Rep 2018; 8:5972. [PMID: 29654241 PMCID: PMC5899174 DOI: 10.1038/s41598-018-23511-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 03/13/2018] [Indexed: 11/13/2022] Open
Abstract
A semi-classical analysis of magneto-thermopower behaviour, namely, the Seebeck and Nernst effect (NE) in quantum wells of IV-VI lead salts with significant extrinsic Rashba spin-orbit coupling (RSOC) is performed in this report. In addition to the spin-dependent Seebeck effect that has been observed before, we also theoretically predict a similar spin-delineated behavior for its magneto-thermal analog, the spin-dependent NE. The choice of lead salts follows from a two-fold advantage they offer, in part, to their superior thermoelectric properties, especially PbTe, while their low band gaps and high spin-orbit coupling make them ideal candidates to study RSOC governed effects in nanostructures. The calculations show a larger longitudinal magneto-thermopower for the spin-up electrons while the transverse components are nearly identical. In contrast, for a magnetic field free case, the related power factor calculations reveal a significantly higher contribution from the spin-down ensemble and suffer a reduction with an increase in the electron density. We also discuss qualitatively the limitations of the semi-classical approach for the extreme case of a high magnetic field and allude to the observed thermopower behaviour when the quantum Hall regime is operational. Finally, techniques to modulate the thermopower are briefly outlined.
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Affiliation(s)
- Parijat Sengupta
- Dept. of Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Yu Wen
- Dept. of Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Junxia Shi
- Dept. of Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA.
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20
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Bathen ME, Linder J. Spin Seebeck effect and thermoelectric phenomena in superconducting hybrids with magnetic textures or spin-orbit coupling. Sci Rep 2017; 7:41409. [PMID: 28139667 PMCID: PMC5282534 DOI: 10.1038/srep41409] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 12/20/2016] [Indexed: 11/09/2022] Open
Abstract
We theoretically consider the spin Seebeck effect, the charge Seebeck coefficient, and the thermoelectric figure of merit in superconducting hybrid structures including either magnetic textures or intrinsic spin-orbit coupling. We demonstrate that large magnitudes for all these quantities are obtainable in Josephson-based systems with either zero or a small externally applied magnetic field. This provides an alternative to the thermoelectric effects generated in high-field (~1 T) superconducting hybrid systems, which were recently experimentally demonstrated. The systems studied contain either conical ferromagnets, spin-active interfaces, or spin-orbit coupling. We present a framework for calculating the linear thermoelectric response for both spin and charge of a system upon applying temperature and voltage gradients based on quasiclassical theory which allows for arbitrary spin-dependent textures and fields to be conveniently incorporated.
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Affiliation(s)
- Marianne Etzelmüller Bathen
- Department of Physics, NTNU, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, N-0316 Oslo, Norway
| | - Jacob Linder
- Department of Physics, NTNU, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
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21
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Kolenda S, Machon P, Beckmann D, Belzig W. Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2016; 7:1579-1585. [PMID: 28144509 PMCID: PMC5238697 DOI: 10.3762/bjnano.7.152] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Accepted: 10/11/2016] [Indexed: 06/06/2023]
Abstract
Background: Thermoelectric effects result from the coupling of charge and heat transport and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron-hole symmetry, which is usually quite small in metal structures. In addition, thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime. Results: We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction. Conclusion: Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to the physics of superconductor/normal-metal microrefrigerators. The spin-dependent thermoelectric signals in the linear regime are due to the coupling of spin and heat transport, and can be used to design more efficient refrigerators.
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Affiliation(s)
- Stefan Kolenda
- Karlsruher Institut für Technologie (KIT), Institut für Nanotechnologie, P.O. Box 3640, D-72021 Karlsruhe, Germany
| | - Peter Machon
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
| | - Detlef Beckmann
- Karlsruher Institut für Technologie (KIT), Institut für Nanotechnologie, P.O. Box 3640, D-72021 Karlsruhe, Germany
| | - Wolfgang Belzig
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
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22
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Kleeorin Y, Meir Y, Giazotto F, Dubi Y. Large Tunable Thermophase in Superconductor - Quantum Dot - Superconductor Josephson Junctions. Sci Rep 2016; 6:35116. [PMID: 27734919 PMCID: PMC5062082 DOI: 10.1038/srep35116] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 09/22/2016] [Indexed: 11/09/2022] Open
Abstract
In spite of extended efforts, detecting thermoelectric effects in superconductors has proven to be a challenging task, due to the inherent superconducting particle-hole symmetry. Here we present a theoretical study of an experimentally attainable Superconductor - Quantum Dot - Superconductor (SC-QD-SC) Josephson Junction. Using Keldysh Green's functions we derive the exact thermo-phase and thermal response of the junction, and demonstrate that such a junction has highly tunable thermoelectric properties and a significant thermal response. The origin of these effects is the QD energy level placed between the SCs, which breaks particle-hole symmetry in a gradual manner, allowing, in the presence of a temperature gradient, for gate controlled appearance of a superconducting thermo-phase. This thermo-phase increases up to a maximal value of ±π/2 after which thermovoltage is expected to develop. Our calculations are performed in realistic parameter regimes, and we suggest an experimental setup which could be used to verify our predictions.
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Affiliation(s)
- Yaakov Kleeorin
- Department of Physics, Ben-Gurion University of the Negev, Beer Sheva, 84105, Israel
| | - Yigal Meir
- Department of Physics, Ben-Gurion University of the Negev, Beer Sheva, 84105, Israel
- The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, 84105, Israel
| | - Francesco Giazotto
- NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
| | - Yonatan Dubi
- The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva, 84105, Israel
- Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva, 84105, Israel
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23
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Beckmann D. Spin manipulation in nanoscale superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:163001. [PMID: 27001949 DOI: 10.1088/0953-8984/28/16/163001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The interplay of superconductivity and magnetism in nanoscale structures has attracted considerable attention in recent years due to the exciting new physics created by the competition of these antagonistic ordering phenomena, and the prospect of exploiting this competition for superconducting spintronics devices. While much of the attention is focused on spin-polarized supercurrents created by the triplet proximity effect, the recent discovery of long range quasiparticle spin transport in high-field superconductors has rekindled interest in spin-dependent nonequilibrium properties of superconductors. In this review, the experimental situation on nonequilibrium spin injection into superconductors is discussed, and open questions and possible future directions of the field are outlined.
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Affiliation(s)
- D Beckmann
- Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology, 76021 Karlsruhe, Germany
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24
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Kolenda S, Wolf MJ, Beckmann D. Observation of Thermoelectric Currents in High-Field Superconductor-Ferromagnet Tunnel Junctions. PHYSICAL REVIEW LETTERS 2016; 116:097001. [PMID: 26991193 DOI: 10.1103/physrevlett.116.097001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Indexed: 06/05/2023]
Abstract
We report on the experimental observation of spin-dependent thermoelectric currents in superconductor-ferromagnet tunnel junctions in high magnetic fields. The thermoelectric signals are due to a spin-dependent lifting of the particle-hole symmetry, and are found to be in excellent agreement with recent theoretical predictions. The maximum Seebeck coefficient inferred from the data is about -100 μV/K, much larger than commonly found in metallic structures. Our results directly prove the coupling of spin and heat transport in high-field superconductors.
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Affiliation(s)
- S Kolenda
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany
| | - M J Wolf
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany
| | - D Beckmann
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany
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25
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Shelly CD, Matrozova EA, Petrashov VT. Resolving thermoelectric "paradox" in superconductors. SCIENCE ADVANCES 2016; 2:e1501250. [PMID: 26933688 PMCID: PMC4771438 DOI: 10.1126/sciadv.1501250] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 12/24/2015] [Indexed: 06/05/2023]
Abstract
For almost a century, thermoelectricity in superconductors has been one of the most intriguing topics in physics. During its early stages in the 1920s, the mere existence of thermoelectric effects in superconductors was questioned. In 1944, it was demonstrated that the effects may occur in inhomogeneous superconductors. Theoretical breakthrough followed in the 1970s, when the generation of a measurable thermoelectric magnetic flux in superconducting loops was predicted; however, a major crisis developed when experiments showed puzzling discrepancies with the theory. Moreover, different experiments were inconsistent with each other. This led to a stalemate in bringing theory and experiment into agreement. With this work, we resolve this stalemate, thus solving this long-standing "paradox," and open prospects for exploration of novel thermoelectric phenomena predicted recently.
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Affiliation(s)
- Connor D. Shelly
- Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
| | - Ekaterina A. Matrozova
- Laboratory of Cryogenic Nanoelectronics, Nizhny Novgorod State Technical University, Nizhny Novgorod 603950, Russia
| | - Victor T. Petrashov
- Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
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26
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Liao T, Lin J, Su G, Lin B, Chen J. Optimum design of a nanoscale spin-Seebeck power device. NANOSCALE 2015; 7:7920-7926. [PMID: 25865604 DOI: 10.1039/c5nr01738f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A theoretical model of a nanoscale spin-Seebeck power device (SSPD) is proposed based on the longitudinal spin-Seebeck effect in bilayers made of a ferromagnetic insulator and a normal metal. Expressions for the power output and thermal efficiency of the SSPD are derived analytically. The performance characteristics of the nanoscale SSPD are analyzed using numerical simulation. The maximum power output density and efficiency are calculated numerically. The effect of the spin Hall angle on the performance characteristics of the SSPD is analyzed. The choice of materials and the structure of the device are discussed. The optimum criteria of some key parameters of the SSPD, such as the power output density, efficiency, thickness of the normal metal, and the load resistance, are given. The results obtained here could provide a theoretical basis for the optimal design and operation of nanoscale SSPDs.
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Affiliation(s)
- Tianjun Liao
- Department of Physics, Xiamen University, Xiamen 361005, People's Republic of China.
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27
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Silaev M, Virtanen P, Bergeret FS, Heikkilä TT. Long-range spin accumulation from heat injection in mesoscopic superconductors with Zeeman splitting. PHYSICAL REVIEW LETTERS 2015; 114:167002. [PMID: 25955071 DOI: 10.1103/physrevlett.114.167002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Indexed: 06/04/2023]
Abstract
We describe far-from-equilibrium nonlocal transport in a diffusive superconducting wire with a Zeeman splitting, taking into account different spin relaxation mechanisms. We demonstrate that due to the Zeeman splitting, an injection of current in a superconducting wire creates spin accumulation that can only relax via thermalization. This effect leads to a long-range spin accumulation detectable in the nonlocal signal. Our model gives a qualitative explanation and provides accurate fits of recent experimental results in terms of realistic parameters.
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Affiliation(s)
- M Silaev
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
- Department of Theoretical Physics, The Royal Institute of Technology, Stockholm SE-10691, Sweden
| | - P Virtanen
- Low Temperature Laboratory, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
| | - F S Bergeret
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, and Donostia International Physics Center (DIPC), Manuel de Lardizabal 5, E-20018 San Sebastián, Spain
| | - T T Heikkilä
- University of Jyväskylä, Department of Physics and Nanoscience Center, P.O. Box 35 (YFL), FI-40014 Jyväskylä, Finland
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28
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Giazotto F, Heikkilä TT, Bergeret FS. Very large thermophase in ferromagnetic Josephson junctions. PHYSICAL REVIEW LETTERS 2015; 114:067001. [PMID: 25723238 DOI: 10.1103/physrevlett.114.067001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Indexed: 06/04/2023]
Abstract
The concept of thermophase refers to the appearance of a phase gradient inside a superconductor originating from the presence of an applied temperature bias across it. The resulting supercurrent flow may, in suitable conditions, fully counterbalance the temperature-bias-induced quasiparticle current therefore preventing the formation of any voltage drop, i.e., a thermovoltage, across the superconductor. Yet, the appearance of a thermophase is expected to occur in Josephson-coupled superconductors as well. Here, we theoretically investigate the thermoelectric response of a thermally biased Josephson junction based on a ferromagnetic insulator. In particular, we predict the occurrence of a very large thermophase that can reach π/2 across the contact for suitable temperatures and structure parameters; i.e., the quasiparticle thermal current can reach the critical current. Such a thermophase can be several orders of magnitude larger than that predicted to occur in conventional Josephson tunnel junctions. In order to assess experimentally the predicted very large thermophase, we propose a realistic setup realizable with state-of-the-art nanofabrication techniques and well-established materials, based on a superconducting quantum interference device. This effect could be of strong relevance in several low-temperature applications, for example, for revealing tiny temperature differences generated by coupling the electromagnetic radiation to one of the superconductors forming the junction.
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Affiliation(s)
- F Giazotto
- NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa, Italy
| | - T T Heikkilä
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35 (YFL), FI-40014 University of Jyväskylä, Finland and Low Temperature Laboratory, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland
| | - F S Bergeret
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 4, E-20018 San Sebastián, Spain and Donostia International Physics Center (DIPC), Manuel de Lardizabal 5, E-20018 San Sebastián, Spain
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